This application claims the priority to and benefit of Japanese Patent Application No. 2004-59139, filed on Mar. 3, 2004, in the Japanese Intellectual Property Office, and Korean Patent Application No. 10-2004-0074190, filed on Sep. 16, 2004, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference.
1. Field of the Invention
The present invention relates to a proton-conducting electrolyte and a fuel cell using the same.
2. Description of the Related Art
A fluorinated polyethylene sulfonic acid group is widely used in an electrolyte membrane for a fuel cell. The fluorinated polyethylene sulfonic acid group has excellent proton-conducting properties and chemical stability, etc. and is used in various applications such as salt electrolysis, seawater desalination, and water treatment. Electrolyte membranes that contain the fluorinated polyethylene sulfonic acid group are commercially available under various trade names including, Nafion™ Membrane, Flemion™ Membrane, Aciplex™ Membrane, and Dow™ Membrane. However, since these membranes contain fluorine, they are both environmentally unfriendly and expensive.
Polystyrene sulfonic acid, which is used in an ion exchange resin or membrane for water treatment, and a sulfonated aromatic polymer, which is used in a fuel cell, are suggested as possible alternate electrolytes that do not contain fluorine (see, Japanese publication of PCT No. Hei 11-502245; T. Kobayashi, M. Rikukawa, K. Sanui, N. Ogata, Solid State Ionics, Vol. 106, 1998, p 219). However, these compounds may not have sufficient heat resistance and chemical stability to be suitable as an electrolyte in a fuel cell.
It was found that a sulfamidic acid group has the same acidity as a sulfonic acid group and is thermally and chemically stable. The present invention overcomes the previously mentioned problems by providing a specific polymer containing a sulfamidic acid group that may have excellent acidity, ion exchange capacity, proton-conducting properties, membrane-forming capability, heat resistance, and chemical stability. In addition, it may be synthesized at a lower cost in a reduced number of reaction steps and results in a high yield.